Process for preparing esters of unsaturated alcohols from monoesters of saturated 2, 2, 4-trisubstituted-1, 3-diols



United States This application is a continuation-in-part of ourcopending application Serial No. 331,092 filed December 17, 1963, nowabandoned which was co-pending with and a continuation-in-part of ourapplication Serial No. 122,638, filed July 10, 1961, now abandoned.

This invention relates to the chemical arts. More particularly, itrelates to the preparation of organic chemical compounds referred to asesters.

Esters are a well-known class of organic chemical compoundscharacterized by a particular molecular arrangement, the graphic formulaof which is i R'Odl-R Wherein R'O is an alcohol moiety and is acarboxylic acid moiety with R being an organic radical and R being aradical selected from the group consisting of hydrogen and organicradicals.

This invention broadly involves a process for the preparation of estersrepresented by the formula:

wherein each R is a radical independently selected from the groupconsisting of hydrogen and R radicals and each R is a radicalindependently selected from the group consisting of alkyl, cycloalkyl,aryl, alkylaryl and arylalkyl. These esters thus defined are genericallyreferred to herein as carboxylic acid esters of unsaturated2,2,4-trisubstituted alcohols or simply as esters of unsaturated2,2,4-trisubstituted alcohols. Preferably, R is an alkyl group having upto about eight carbon atoms.

Esters of unsaturated 2,2,4-trisubstituted alcohols have utility asintermediates in the preparation of other organic materials useful assynthetic lubricants and plasticizers. Thus, these esters can be reducedand converted to the corresponding alcohols which are useful assynthetic lubricants and plasticizers. Also, esters of unsaturated2,2,4- trisubstituted alcohols can be reacted further as by the oxoreaction to produce esters of hydroxy aldehydes, such as6-isobutyroxy-3,5,5-trimethylhexanal, which are useful as intermediatesin the preparation of synthetic lubricants, plasticizers and polyesters.Hence, these esters of unsaturated 2,2,4-trisubstituted alcohols areuseful compounds.

Heretofore, these esters of unsaturated 2,2,4-trisubstituted alcoholshave been synthesized by a process which comprises completelyesterifying the corresponding saturated 2,2,4-trisubstituted-1,3-diol(or glycol) with a carboxylic acid to form the diester and thenthermally cracking or pyrolysing the diester to the ester of theunsaturated 2,2,4-trisubstituted alcohol. This process is described inthe US. Patent No. 2,941,011, to Hagemeyer et al.

atent This process, however, has several disadvantages. One disadvantageresides in the large quantity of carboxylic acid, which must be employedto obtain complete esterification of the glycol and which subsequentlymust be recovered if a substantially pure end product is desired and/ orif the economics of the process require reuse of the acid. Anotherdisadvantage resides in the fact the thermal cracking step requires hightemperatures (300- 600 C. being mentioned in the Hagemeyer et al.patent) and short contact times (0.01 second to 10 seconds beingdisclosed in this patent). These process conditions call for ratherspecialized, expensive equipment with careful control and frequentregulatory attention by skilled personnel.

Accordingly, there is a need for a process for preparing esters ofunsaturated 2,2,4-trisubstituted alcohols, which avoids thesedisadvantages. An object of this invention is to satisfy this need.

At this point it might be thought that one way to make these esters ofunsaturated 2,2,4-trisubstituted alcohols is to react an organic acidwith the parent unsaturated 2,2,4- trisubstituted alcohol. The problemhere, however, is in obtaining the parent unsaturated2,2,4-trisubstituted alcohol. Such alcohols are not readily obtainable.On the other hand the corresponding saturated2,2,4-trisubstituted-1,3-diols are readily obtainable. However, asreported by Perry et al., J. M. Chem. Soc., 80, 3618 (1958), attempts todehydrate 2,2,4-trisubstituted-1,3-diols in the presence of acidcatalysts produced only substituted furans and 2,3,4-trisubstitutedaldehydes with no conversion to the unsaturated alcohols. Apparently,2,2,3-trisubstituted- 1,3-diols can be dehydrated in the presence ofacid catalysts but 2,2,4-trisubstituted-1,3-diols cannot. Consequently,preparation of esters of unsaturated 2,2,4-trisubstituted alcohols byesterification of the parent unsaturated 2,2,4-trisubstituted alcoholsdoes not now appear commercially feasible. Hence, an object of thisinvention is to provide a process for preparing esters of unsaturated2,2,4-trisubstituted alcohols other than by the esterification of theparent alcohols.

As just mentioned, saturated 2,2,4-trisubstituted-1,3- diols are readilyobtainable. They are easily synthesized by the aldol condensation of thecorresponding alphasubstituted aliphatic aldehyde followed by reductionof the aldol to the glycol. Monoesters of these glycols can be preparedby partial esterification with carboxylic acids, their anhydrides ortheir chlorides with esterification occurring predominantly at theprimary hydroxyl group. These monoesters can also be obtained by thetrimeric condensation of readily available alpha, alpha-disubstitutedacetaldehydes in the presence of a basic catalyst such as, for example,an alkali metal alkoxide, as described in US. Patent 3,091,632. Hence,these monoesters are readily obtainable materials. Another object ofthis invention is to provide a process for the preparation of esters ofunsaturated 2,2,4-trisubstituted alcohols from the correspondingmonoesters of saturated 2,2,4-trisubstituted-1,3-diols.

A further object of this invention is to provide such a process which iscommercially practical, which is economical and which is inherentlysimple.

These and other objects are achieved by this invention.

In summary, this invention comprises a process based on the discoverythat carboxylic acid esters of unsaturated 2,2,4-trisubstituted alcoholsare synthesized by subjecting the corresponding monoesters of saturated2,2,4-trisubstituted-1,3-diols to catalytic dehydration with certaincompounds as dehydration catalysts. It has been discovered thatcatalytic dehydration is accomplished at high yields and conversions bycontacting under certain easily controlled and regulated temperaturesand time conditions a saturated 2,2,4-trisubstituted glycol monoester(represented by the following generic formula) with a catalytic quantityof a highly acidic, non-volatile compound. The highly acidic,non-volatile compounds that can be employed in the invention aresulfuric acid, alkyl and aryl sulfates, alkyl and aryl sulfonic acids,phosphoric acid, alkyl and aryl phosphates, alkyl and aryl phosphonicacids, alkyl and aryl phosphinic acids, pyrophosphoric acid,metaphosphoric acid and acetylsulfoacetic acid. Representative examplesof these compounds are ethyl sulfate, benzyl sulfate, methane-sulfonicacid, paratoluene sulfonic acid, chloronaphth'alene-sulfonic acid, ethylphosphate, phenyl phosphate, methyl phosphonic acid, phenyl phosphonicacid, trifluoromethanephosphonic acid, and dibenzylposphinic acid.Acetyl sulfoacetic acid is prepared according to the procedure set forthin U.S. Patent 2,411,823. Preferably, the above alkyl groups, which maybe substituted, are lower alkyl of from 1 to 4 carbon atoms and the arylgroups are substituted phenyl and naphthalene radicals. A preferredgroup of specific dehydrating catalysts are sulfuric acid,p-toluene-sulfonic acid, naphthalene sulfonic acid, phosphoric acid andpyrophosphoric acid. Of course, the use of a com-pound which ishydrolyzed in the process to an acid of the type mentioned herein is tobe considered within the scope of the invention.

As stated above Perry et al. found that 2,2,4-trisu-bstituted-l,3-diolscould not be dehydrated with acid catalysts to yield the unsaturatedesters shown in column 1. Whitmore, Organic Chemistry, Van Nostrand Co.,p. 128 (1937) and Whitmore, J. Am. Chem. Soc., 54, 3279 (1939) disclosethat all reagents, including dehydrating agents, which would be expectedto remove or replace the hydroxyl group from neopentyl alcohol gavelittle or none of the expected product, but caused rearrangement of theneopentyl structure. In the second of the Whitmore references citedabove, on page 3280, it is disclosed that dehydration ofisopropyl-tertiary-butylcarbinol gave none of the expected product,2,2,4-trimethylpentene-3. Thus, it was surprising to discover that theacyloxy derivatives of similar neopentyl alcohols could be dehydratedaccording to our novel process as shown below. The unexpectedness of ourprocess is readily apparent from the chemical reactions diagrammedbelow.

wherein R and R are as defined above;

Prior art Whitmore OH; OH CH; (3H3 CH3 CHg-CH-CH-(f-OH; cH -c=oH-boH CH3H3 Prior art Perry CH3 ?H CH3 CH3 ([31:13 CHr-CH-CH-( J-CHZOHCHr=CH-(|3CH2OH H3 CH3 From the above reactions, it can be seen thatapplicants obtain the desired 2,2,4atrisubstituted-ester when amonoester of a 2,2,4-trisubstituted-l,4-diol is dehydrated according totheir novel process. It can also be seen that Whitmore and Perry et al.were not able to obtain a product similar to that obtained fromapplicants process by the dehydration of alcohols and glycols verysimilar to the glycol monoesters employed in the invention.

When the process of our invention is considered in view of the prior artrepresented by the Whitmore and Perry et al. references cited above, itis apparent that the dehydration of a monoester of a2,2,4-trisubstituted- 1,3-diol to yield the unsaturated ester shown incolumn 1 was not predictable. Thus, the discovery that unsaturatedesters could be prepared by the acid catalyzed dehydration of monoestersof 2,2,4-trisubstituted-1,3-diols was unexpected in view of theinability of Perry et al. and Whitmore to obtain similar unsaturatedcompounds from the alcohols and glycols of which the monoesters used inthe invention are derivatives.

The saturated 2,2,4-trisubstituted glycol monoesters employed in theprocess of this invention are represented by the generic formula:

wherein each R is a radical independently selected from the groupconsisting of hydrogen and R radicals and each R is a radicalindependently selected from the group consisting of alkyl, cyclo'alkyl,aryl, alkylaryl and arylalkyl radicals. The R and R radicals in thisformula are identical to the respective R and R radicals at molecularlycorresonding positions in the formula set out at the beginning of thisspecification for the esters of unsaturated 2,2,4-trisubstitutedalcohols. Especially preferred 2,2,4-trisubstituted glycol monoestersfor use in the process of our invention are those of the foregoingformula in which R is lower alkyl, e.g., alkyl of 1 to about 4 carbonatoms. Typical saturated glycol monoesters represented by this graphicformula and employed in the process of this invention are:

3-hydroxy-2,2-dimethylhexyl acetate 3-hydroxy-2,2,4-trimethylpentylacetate 2-ethyl-3-hydroxy-2-methylhexyl acetate3-hydroxy-2,2,4-trimethylpentyl isobutyrate2-ethyl-3-hydroxy-2,4-dimethylhexyl Z-methylbutyrate2-butyl-2,4-diethyl-3-hydroxyoctyl 2-ethy1hexoate2,4-diethyl-3-hydroxy-2-isobutylheptyl 2-ethyl-4- methylpentoate3-hydroxy-Z,2,4-triethylhexyl Z-ethylbutyrate2-cyclohexyl-3-hydroxy-2,4-dimethylhexyl 2-cyclohexylpropionate3-hydroxy-2,2,4-tricyclohexylbutyl 2,2-dicyclohexyl acetate2-methyl-3-hydroxy-2,4- di(para-methylphenyl)-pentyl 2(para-methylphenyl propionate3-hydroxy-2,2,4,4-tetra(para-methylphenyl)butyl 2,2-

di (para-methylphenyl) acetate Other glycol monoesters represented bythe graphic formula can be used under the concepts of this invention andwill be readily recognized by those in the exercise of ordinary skill inthe art.

These saturated monoesters of 2,2,4-trisubstituted- 1,3-diols can beprepared by the partial esterification of the corresponding glycols, anumber of which are, as mentioned in a preceding paragraph, easilysynthesized by the aldol condensation of the correspondingalphasubstituted aliphatic aldehyde followed by reduction of the aldolto the glycol. Preferably, however, they are obtained by the trirnericcondensation of a corresponding alpha-substituted aliphatic aldehyde inthe presence of a basic catalyst, such as, for example, an alkali metalallcoxide. Crude glycol monoester from the condensation reaction iswashed and the unreacted aldehyde recovered as by azeotropicdistillation or by other suitable ways. The stripped crude glycolmonoester is then decanted, and if desired, is used in the process ofthis invention without further purification. On the other hand, thecondensation products can be separated by distillation and only thepurified glycol monoester employed in the process of this invention.

The dehydration catalyst functions under the conditions of the processof this invention to cause the glycol monoester to dehydrate and becomeunsaturated at the 3 position of the resultant 2,2,4-trisubstitutedalcohol moiety. As mentioned above, the phosphorous and sulfur compoundsthat are useful dehydration catalysts in our process are characterizedby being highly acid and nonvolatile under the reaction conditions ofthe process. Volatile compounds such as strong halogen acids, even ifthey are elfective as dehydration catalysts, are to be avoided under theconcepts of this invention. The members of the group of specificdehydration catalysts are somewhat exclusive in effect inasmuch as othernonvolatile compounds such as potassium acid sulfate, oxalic acid, boricacid, silica gel, alumina and zinc chloride are not effective under theconditions of this invention.

Concentration of the dehydration catalyst is preferably at least thatwhich will cause dehydration in 2 to 24 hours, desirably 4 to 8 hours,at the reaction temperature involved. An excessive concentration ofdehydration catalyst promotes a competing ester interchange reaction andthus high conversions to the glycol and glycol diester with resultingdecreased yields of the desired ester of an unsaturated2,2,4-trisu'bstituted alcohol. Hence, the concentration of thedehydration catalyst is established and maintained as low aspracticable. Of course, too low a concentration of the dehydrationcatalyst results in a dehydration reaction which is too slow to bepractical. In general, satisfactory results are obtained with thecatalyst concentration being in a range substantially from 0.03 to 3% byweight of the glycol monoester.

Reaction temperature is an important aspect of this invention. Ingeneral, the temperature of dehydration is established and maintainedbelow the boiling point of the saturated glycol monoester. Preferably,the temperature of dehydration is established and maintained in a rangesubstantially from 90 to 160 C. with the optimum range beingsubstantially from 110 to 135 C. At a dehydration temperature below 90C. the conversion of glycol monoester to the corresponding ester of anunsaturated alcohol is very low and the glycol monoester is converted byester interchange to an equilibrium mixture of glycol, glycol monoesterand glycol diester. At a dehydration temperature above 160 C. thedehydration of the glycol monoester is nearly complete but the principalproducts of the reaction include the ester of the unsaturated alcohol,the acid, substituted tetrahydrofurans and other products which areformed by an initial cracking or rearrangement reaction.

Temperature control can be achieved by carrying out the dehydrationreaction of this invention in the liquid phase with an inert diluent, inthe liquid phase at subatmospheric pressure, in the vapor phase atatmospheric pressure or in the vapor phase at subatmospheric pressure.Each of these techniques is particularly suited to the controlling ofreaction temperature. However, for ease and economy of operation it ispreferred to conduct the dehydration reaction in the liquid phase with adiluent. Since the boiling point of the reaction mixture is governed bythe concentration of the diluent, regulation of the concentration of thediluent in the reaction mixture is a convenient way of controlling thereaction temperature. A :diluent which boils near or above the desiredreaction temperature can be used if the boiling point of the reactionmixture is controlled by establishing and maintaining the pressure inthe reactor at a value less than one atmosphere. It is preferred to usea diluent which is inert under the reaction conditions of this process,which is insoluble in water and which forms an azeotrope with water.Examples of suitable diluents are benzene, toluene, isobutylisobutyrate, hexane and cyclohexane.

In performing a preferred embodiment of the process of this inventionunder liquid phase and diluent conditions, the glycol monoester, diluentand dehydration catalyst are mixed at ambient temperature in theproportions which will result in a dehydration temperature ofsubstantially 90160 C. and usually substantially -135 C. This mixture isthen introduced into a suitable dehydration reactor. Such a reactor is avessel fitted with an overhead condenser, overhead condensate decanterand means for heating the contents of the dehydration reactor to theboiling point. The temperature of the mixture in the reactor isestablished and maintained at the boiling point, usually 110135 C.,until sub. stantially all the water resulting from the dehydrationreaction is removed as an azeotrope with the diluent. The water isseparated from the diluent continuously in the decanter and the diluentis returned to the reactor. At the conclusion of the reaction, which isevidenced by the fact no more water collects in the decanter at refluxtemperature, the reaction mixture is cooled and then discharged from thereactor. The crude product preferably is worked up as by washing withwater or with an aqueous solution of a weak base such as, for example,sodium carbonate. The essentially pure ester of the unsaturated alcoholpreferably is then obtained as by distillation preferably atsubatmospheric pressure.

The process of this invention can be carried out on a continuous basis.This is accomplished by introducing glycol monoester and a quantity ofdehydration catalyst of the group equal to substantially 0.03 to 3% byweight of the monoester into a reactor with a packed distillationcolumn. The reactor forms a reaction zone. The temperature of theresulting reaction mixture is established and maintained in a range ofsubstantially 100-160 C., but below the boiling point of the glycolmonoester. As a result dehydration of the glycol monoester occurs andthe corresponding unsaturated ester and water are formed. The water andunsaturated ester distill off from the reaction mixture and arecollected. As this takes place glycol monoester is introduced into thereactor at a flow rate at which a substantially constant level ofreaction mixture is established and maintained in the reactor.

This invention is further illustrated by the following examples ofvarious aspects of this invention, including specific embodimentsthereof. This invention is not limited to these embodiments unlessotherwise indicated.

EXAMPLE 1 This example illustrates the synthesis according to thisinvention of a 2,2-dimethyl-3-hexenyl ester.

A mixture of 500 milliliters of toluene, 400 milliliters (2.00 moles) of3-hydroxy-2,Z-dimethylhexyl acetate and 0.3 milliliter (0.0054 mole) ofconcentrated sulfuric acid is introduced into the base of a dehydrationreactor. This dehydration reactor comprises a IO-bubble plate columnfitted with an overhead condenser and decanter and a base distillingflask fitted with a thermowell and heated by an electric mantle. Themixture is refluxed in the flask at a flask temperature of 130 C. At theend of 4.5 hours it is typical for no more water to collect in thedecanter, thus indicating dehydration is essentially complete.

The reaction mixture is cooled, neutralized, washed and distilled atatmospheric pressure. The product thus obtained, which consistsessentially of the ester of the unsaturated 2,2,4-trisubstitutedalcohol, distills typically at 186189 C. and weighs 298.3 grams (1.755moles). This ester, 2,2-dimethyl-3-hexenyl acetate, can be identified bysaponification equivalent and comparison of the physical properties ofit and of an authentic sample. A typical yield of this ester is 87.8mole percent.

EXAMPLE 2 This example illustrates the synthesis according to theprocess of this invention of a 2-ethyl-2-methyl-3-hexenyl ester.

A mixture of 500 milliliters of toluene, 400 milliliters (1.86 moles) of2-ethyl-3-hydroxy-2-methylhexyl acetate and 0.3 milliliter (0.0054 mole)of concentrated sulfuric acid are introduced into the base flask of theequipment of Example 1. The mixture is heated to reflux temperature.Dehydration is generally essentially complete in 6 hours at a basetemperature of 128-133 C.

The reaction mixture is cooled, neutralized, washed and distilled atreduced pressure. The product thus obtained consists essentially of theester of the unsaturated alcohol, 2-ethyl-2-methyl-3-hexenyl acetate.The product distills typically at 90100 C. at a pressure of 4millimeters of mercury and typically Weighs 310 grams (1.685 moles). Theester can be identified by saponification equivalent and comparison ofphysical properties of it and an authentic sample. A typical yield ofthis ester of an unsaturated 2,2,4-trisubstituted alcohol is 90.8 molepercent.

EXAMPLE 3 This example illustrates the synthesis according to thisinvention of 2,2,4-trimethyl-3-pentenyl isobutyrate from3-hydroxy-2,2,4-trimethylpentyl isobutyrate.

A mixture of 300 milliliters of toluene, 400 milliliters (1.74 moles) of3-hydroxy-2,2,4-trimethylpentyl isobutyrate and 0.3 milliliter (0.0054mole) of concentrated sulfuric acid are fed into the base of thedehydration reactor of Example 1. The mixture is heated to refluxtemperature and refluxed for 7 hours. During this time the base orreaction temperature typically rises from 130-138 C. while 29.5milliliters (1.64 moles) of water typically are col lected in theoverhead decanter. Dehydration is essentially complete in 7 hours asevidenced by the fact substantially no more water collects in theoverhead trap.

The reaction mixture is cooled, washed with dilute sodium carbonate andwater, then distilled at reduced pressure. The product thus obtainedconsists essentially of 2,2,4 trimethyl 3 pentenyl isobutyrate. Theproduct typically distills at 7882 C. at millimeters mercury pressureand weighs 297 grams (1.50 moles). This represents a yield of 86.2 molepercent. Identification of this product can be accomplished by thedetermination of saponification equivalent and by comparison of physicalproperties of it with an authentic sample.

EXAMPLE 4 According to the procedure set forth in Example 3, a mixtureof 300 ml. toluene, 400 ml. (1.74 moles) 3-hydroxy 2,2,4 trimethylpentylisobutyrate and a catalyst shown in the table below were refluxed untilthe formation of water is completed. The following table shows the highyields of desired product that are obtained from our novel process:

From this table, it can also be seen that many compounds ordinarily usedas dehydration catalysts do not dehydrate 3hydroxy-2,2,4-trimethylpentylisobutyrate.

EXAMPLE 5 This example illustrates the influence of a lower than optimumtemperature in the synthesis according to this invention of2,2,4-trimethyl-3-pentenyl isobutyrate from3-hydroxy-2,2,4-trimethylpentyl isobutyrate.

A mixture of 300 milliliters of benzene, 400 milliliters (1.74 moles) of3hydroxy-2,2,4-trimethylpentyl isobutyrate and 0.3 milliliter (0.0054mole) of concentrated sulfuric acid are fed into the dehydration reactordescribed in Example 1. The mixture is refluxed for 2 hours .A typicalbase or reaction temperature is 99 C. During this time generally nowater collects in the overhead decanter. Fifty milliliters of benzeneare then removed from the mixture by distillation. Typically thereaction temperature rises to C. The mixture is refluxed for 24 hourswhile typically 18 milliliters (1.0 mole) of water collect in theoverhead decanter.

The reaction mixture is cooled, washed with dilute sodium carbonate andwater and then distilled at reduced pressure. The crude product isthereby separated into fractions which typically comprise 250milliliters of a benzene fraction, 190.1 grams (0.96 mole) of a fractionconsisting essentially of the ester of the unsaturated 2,2,4-trisubstituted alcohol (2,2,4-tri'methyl-3-pentenyl isobutyrate), whichfraction boils at 92-95 C. at 10 millimeters mercury pressure, 27.7grams (0.190 mole) of a fraction consisting essentially of the glycol(2,2,4-trimethylpentyll,3-diol), which fraction boils at 102-105 C. at10 millimeters mercury pressure, 75.2 grams (0.398 mole) of a fractionconsisting essentially of the glycol monoester (3 hydroxy2,2,4-trimethylpentyl isobutyrate), which fraction boils at -128 C. at10 millimeters, and 59.0 grams (0.206 mole) of a fraction consistingessentially of the glycol diester(2,2,4-trimethylpentyl-1,3-diisobutyrate), which fraction boils atl40-150 C. at 10 millimeters mercury pressure. Identification of theseproducts can be accomplished by hydroxyl determination, saponificationand comparison of physical properties of the fractions with those ofauthentic samples. A typical yield of the ester of the unsaturated2,2,4-trisubstituted alcohol is 68.8 mole percent while a typical yieldof the ester interchange products is 28.4 mole percent.

EXAMPLE 6 This example illustrates the influence of a higher thanoptimum temperature in the synthesis according to this invention of2,2,4-tri-methyl-3-pentenyl isobutyrate from 3-hydroxy-2,2,4-trimethylpentyl isobutyrate.

A mixture of 300 milliliters of isobutyl isobutyrate, 400 milliliters1.74 moles) of 3 hydroxy-2,2,4-trimethylpentyl isobutyrate and 5 grams(0.029 mole) of paratoluenesulfonic acid is charged into the dehydrationreactor described in Example 1. The mixture is heated to boiling, j

producing a reaction temperature typically of -162 C. Dehydration istypically essentially complete in 5 hours.

The reaction mixture is cooled, washed and distilled at atmosphericpressure. There is thus obtained a product typically weighing 68.5 grams(0.54 mole) and typically boiling at 120-135 C. This product consistsessentially of tetramethyltetrahydrofuran. The remaining reactionmixture is then distilled at reduced pressure (10 millimeters, mercury)to give typically 300 milliliters of a fraction consisting essentiallyof isobutyl isobutyrate, which fraction boils at 3842 C., 101.5 grams(0.513 mole) of a fraction consisting essentially of the ester of theunsaturated 2,2,4-trisubstituted alcohol (2,2,4-trimethyl-3-pentenylisobutyrate), 14.8 grams (0.10 mole) of a fraction consistingessentially of the glycol 2,2,4-trimethylpentyl-1,3-diol and 142 grams(0.49 mole) of a fraction consisting essentially of the glycol diester2,2,4-trimethylpentyl-1,3-diisobutyrate. A typical yield of the desiredproduct, the ester of the unsaturated 2,2,4-trisubstituted alcohol, is29.5 mole percent. A typical yield of the dehydration plus rearrangementproduct (tetramethyltetrahydrofiuran) is 30.8 mole percent. A typicalyield of the ester interchange products (the glycol and the glycoldiester) is 34.3 mole percent. The isobutyl isobutyrate did not reactunder these conditions.

9 EXAMPLE 7 This example illustrates the synthesis according to thisinvention of a 2-ethyl-2,4-dimethyl-3 hexenyl ester from2-ethyl-3-hydroxy-2,4-dirnethylhexyl ester.

A mixture of 500 milliliters of toluene, 300 milliliters (1.10 moles) of2-ethyl-3-hydroxy-2,4-dimethylhexyl 2- methylbutyrate and 1 milliliter(0.018 mole) of concentrated sulfuric acid are charged into thedehydration reactor described in Example 1. The mixture is heated toreflux temperature. The mixture is refi-uxed for 2.5 hours at a reactiontemperature of 120-125" C.

At the end of this time, dehydration being typically essentiallycomplete, the reaction mixture is cooled, washed and distilled atreduced pressure. The product thus obtained, consists essentially of theester of the unsaturated 2,2,4-trisubstituted alcohol (2 ethyl 2,4dimethyl 3- hexenyl 2-methylbutyrate). The product distills typically at100110 C. at 3 millimeters mercury pressure and typically weighs 235.5grams (0.981 mole). Identification of this product can be accomplishedby saponification equivalent and comparison of its physical propertieswith those of an authentic sample. A typical yield of the ester of theunsaturated 2,2,4-trisubstituted alcohol is 89.1 mole percent.

EXAMPLE 8 This example illustrates the practice of the process of thisinvention on a continuous basis.

An initial change of 2.5 liters of the glycol monoester,3-hydroxy-2,2,4-trimethylpentyl isobutyrate, and 3.8 milliliters (0.3weight percent) of concentrated sulfuric acid is introduced to the baseheater of a packed distillation column. Heat is applied to the changeand distillation pressure is lowered to 15-25 millimeters of mercury.When the base temperature has reached 125-130" C., glycol monoester isrun into the base heater at an average rate of 350 milliliters per hour.At this flow rate a constant level of reaction mixture and a catalystconcentration of 0.2-0.3 weight percent are established and maintainedin the base heater. In this run the total change of glycol monoester is9 liters (39.25 moles). Water and reaction products are continuouslydistilled overhead as they form, the temperature at the top of thecolumn typically being 90110 C. At the end of this run a crude productis obtained which typically weighs 5880 grams and which contains at aconcentration of about 86% by weight of the product the ester of theunsaturated 2,2,4-trisubstituted alcohol (2,2,4- tri-methyl-3-pentenylisobutyrate) On redistillation of the crude product to which has beenadded the washed contents of the base heater, 5057 grams (25.54 moles)of the ester of the unsaturated 2,2,4 trisubstituted alcohol typicallydistill over at 78-82 C. at millimeters mercury pressure and 2359 grams(10.93 moles) of unreacted glycol monoester typically distill over at110-120 C. at 5 millimeters mercury pressure. Hence, conversion of theglycol monoester is typically about 72 mole percent while the yield ofester of the unsaturated alcohol is typically 90.2 mole percent. Withoutfurther purification the ester of the unsaturated 2,2,4- trisubstitutedalcohol is suitable for further reaction, such as hydrogenation toisobutanol and 2,2,4-trimethylpentanol.

EXAMPLE 9 This example illustrates the vapor phase operation of ourprocess.

The glycol monoester, 3-hydroxy-2,2,4-trimethylpentyl isobutyrate, waspassed over a catalyst bed. The vaporizer and catalyst bed weremaintained at subatmospheric pressure to provide a vapor phase reaction.The product was neutralized, washed and distilled. The yield to2,2,4-trimethyl-3-pentenyl isobutyrate is calculated from the weight ofthe fraction which boils at 77-82 C. at 5 mm. mercury pressure and theweight of unreacted glycol monoester, which boils at 128-132 C. at 5 mm.mercury pressure. Contact time is calculated in the usual way, based onthe volume of the empty catalyst tube. The results of 'five runs and thecatalyst and reaction conditions employed in each of the runs are shownin the following table:

By following the steps under conditions similar to those to theseexamples the glycol monoester 3-hydroxy-2,2,4- trimethylpentyl acetateis converted to 2,2,4-trimethyl- 3-pentenyl acetate;2-ethyl-3hydroxy-2,4-dimethylhexyl acetate is converted to2-ethyl-2,4-dimethylhexenyl acetate; 2-'butyl-2,4-diethyl-3-hydroxyoctyl2-ethylhexoate is converted to 2-butyl-2,4-diethyl-3-octenyl2-ethylhexoate; 2,4 diethyl-3-hydroxy-2-isobutylheptyl2-ethyl-4-methylpentoate is dehydrated to2,4-diethyl-2-isobutyl-3-heptenyl 2-ethyl-4-methylpentoate;3-hydroxy-2,2,4-trimethylhexyl Z-ethylbutyrate is converted to2,2,4-trimethyl-3- hexenyl 2-ethylbutyrate;2-cyclohexyl-3-hydroxy-2,4-dimethylhexyl 2-cyclohexylpropionate isconverted to 2- cyclohexyl 2,4 dimethyl-3-hexenyl2-cyclohexylpropionate; 3-hydroxy-2,2,4-tricyclohexylbutyl2,2-dicyclohexylacetate is converted to 2,2,4-tricyclohexyl-3-butenyl2,2- dicyclohexylacetate;2-methyl-3-hydroxy-2,4-di(paramethylphenyl)-pentyl2-(para-methylphenyl)-propionate is dehydrated to 2methyl-2,4-di(para-methylphenyl)-3-pentenyl2-(para-methylphenyl)-propionate; 3-hydroxy-2,2- 4,4tetra(para-methylphenyl)butyl 2,2 di(para-methylphenyl) acetate isconverted to 2,2,4,4-tetra(para-methylphenyl)-3-butenyl2,2-di(para-methylphenyl)-acetate; and other monoester of2,2,4-trisubstituted-1,3-diols not listed herein are converted to thecorresponding esters of unsaturated 2,2,4-trisubstituted alcohols.

Thus, this invention provides a simple and direct process for producingcarboxylic acid esters of unsaturated 2,2,4-trisubstituted alcohols fromthe corresponding saturated 2,2,4-trisubstituted-1,3-diol monoesters.

Other advantages, features and embodiments of this invention will occurto those in the exercise of ordinary skill in the art upon reading theforegoing specification. In this connection, while this invention hasbeen described in detail with reference to specific embodiments thereof,variations and modifications thereof can he effected within the spiritand scope of the invention as described and claimed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A process for making an ester of an unsaturated 2,2,4-trisubstitutedalcohol of the formula wherein each R is a radical independentlyselected from the group consisting of hydrogen and R radicals and each Ris a radical independently selected from the group consisting of alkyl,cycloalkyl, aryl, alkylaryl and arylalkyl radicals, which comprises:contacting a glycol monoester of the formula R OH If. 0 RCHCH-GCHg0-iL-Rwherein R and R are as specified above with a highly acidic, nonvolatilecompound selected from the group consisting of sulfuric acid, alkyl andaryl sulfates, alkyl and aryl sulfonic acids, phosphoric acid, alkyl andaryl phosphates, alkyl and aryl phosphonic acids, alkyl and arylphosphinic acids, pyrophosphoric acid, meta phosphoric acid andacetylsulfoacetic acid at a catalytic concentration for a period ofabout 2 to about 24 hours at a temperature of about 90 C. to about 160C.

2. A process according to claim 1 wherein R is an alkyl group having oneto about eight carbon atoms.

3. A process according to claim 2 wherein the concentration of saidhighly acidic, nonvolatile compound is about 0.03 to about 3%.

4. A process according to claim 3 wherein said contacting period issubstantially 4 to '8 hours and said temperature is from about 110 toabout 135 C.

5. A process according to claim 4 wherein said highly acidic,nonvolatile compound is sulfuric acid, phosphoric acid, p-toluenesulfonic acid, pyrophosphoric acid, chloronaphthalene sulfonic acid,acetyl, sulfoacetic acid, ethyl phosphate or trifluoromethane phosphoricacid.

6. A process according to claim 5 wherein the glycol monoester is3-hydroxy-2,2,4-trimethylpentyl isobutyrate and the ester of anunsaturated 2,2,4-trisubstituted alcohol is 2,2,4-trimethyl-3-pentenylisobutyrate.

7. A process according to claim 5 wherein the glycol 12 monoester is2-ethyl-3-hydroxy-2,4-dimethylhexyl 2-methylbutyrate and the ester of anunsaturated 2,2,4-trisubstituted alcohol is2-ethyl-2,4-dimethyl3-hexenyl 2-methylbutyrate.

8. A process according to claim 5 wherein the glycol monoester is3-hydr0xy-2,2,4-trimethylpentyl acetate and the ester of an unsaturated2,2,4-trisubstituted alcohol is 2,2,4-trimethyl-S-pentenyl acetate.

9. A process according to claim 5 wherein the glycol monoester is2-ethyl-3-hydroxy-2,4-dimethylhexyl acetate and the ester of anunsaturated 2,2,4-trisubstituted alcohol is2-ethyl-2,4-dimethyl-3-hexenyl acetate.

10. A process according to claim 5 wherein the glycol monoester is2-ethyl-3-hydroxy-2,4-dimethylhexyl isobutyrate and the ester of anunsaturated 2,2,4-trisubstituted alcohol is2-ethyl-2,4-dimethyl-3-hexenyl isobutyrate.

References Cited UNITED STATES PATENTS 2,226,645 12/1940 Thomas 260486LORRAINE A. WEINBERGER, Primary Examiner.

V. GARNER, Assistant Examiner.

Washington. 0.0. 20231 UNITED STATES PATENT OFFICE ERTIFICATE 0FCORRECTION Patent No. 3,408,388 October 29, 1968 Hug-h John Hagemeyer,Jr., et al.

It is certified the} error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 3, line 15, "dibenzylposphinic" should read dibenzylphosphinicColumn 7, line 63, "Zinc" should read Zinc chloride Signed and sealedthis 10th day of March-1970.

(SEAL) Attest:

Edward M. Fletcher. Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

1. A PROCESS FOR MAKING AN ESTER OF AN UNSATURATED 2,2,4-TRISUBSTITUTEDALCOHOL OF THE FORMULA